Bengaluru: Scientists studying plant growth in the Kaziranga region may have found the missing link in calculating carbon dioxide in the air to calibrate climate change strategies.
An Indian Institute of Tropical Meteorology (IITM) team, in collaboration with Kaziranga forest officials, has found that monsoon is not the best season for carbon uptake by plants and trees. In fact, forests absorb the highest levels of carbon dioxide in the pre-monsoon season, the study found. The first of its kind, the study was published in Agricultural and Forest Meteorology.
In the monsoon season, thick clouds hovering over the Kaziranga region block sunlight. This limits photosynthesis and subsequently carbon dioxide uptake. But in the pre-monsoon period, most of the sun’s radiation is received by plants to help photosynthesis.
“This information is missing in climate mitigation strategies,” Pramit Kumar Deb Burman, lead author of the study, told ThePrint.
Carbon uptake is a process by which carbon dioxide is absorbed and stored inside living organisms. The study also found carbon uptake and its relationship with the monsoon is not the same for all Indian ecosystems.
So far, the carbon budget calculation globally lacks data from the ground, especially in countries like India. The lack of data weakens accurate national carbon cycle assessments, and even climate change mitigation strategies. This study solved the carbon budget puzzle with regional information, through observation on the ground, according to Pramit Kumar Deb Burman, lead author of the study.
Missing link found
Conventionally, scientists explore different ways to calculate carbon emissions. For example, satellite data that looks for reflected radiation, calls for a top-down approach. The other way is to observe the ground level energy exchange and temperature through local sensors, and extend the finding to a global level.
“We work in a bottom-up fashion, in the sense that we first get the observation and then we upskill to the global level. There are also people like space scientists and remote sensing people who actually look into it from the top,” said Burman.
The importance of ground-based land observations has been understood only in the past decade as land has been the bigger carbon sink than the ocean.
To calculate a carbon budget, it is equally important to figure out how much carbon plants will ‘respire’ back, apart from the carbon they retain in their body mass. “The only way to know about this thing is to actually use some ground-based observations, which we have done,” Burman said.
The study is the missing link between different approaches through data from sensors installed in the ground as opposed to satellite data. The next step is to validate the existing models against the findings to complete the carbon budget puzzle.
It took four years for the team led by Burman to compile the data and solve the complex physics equation to calculate the carbon uptake. But that was not enough to prove their findings.
How Physics met Life Science
The researchers had to validate their calculated data, with the observed data on plant growth in the Kaziranga region.
The calculations were done using the Eddy Covariance technique, a method to analyse the exchange of gases and energy in the atmosphere with the help of different instruments such as a gas analyser and a sonic anemometer that measures the wind and temperature. Unlike satellite measurements, for this study, data was observed locally using ground-based instruments to avoid scattering and other losses.
According to Burman, satellites provide one measurement every day, whereas in their study, data was collected ten times in a second.
“We also measured the soil temperature, what is the CO2 flux coming out of soil, because soil also has got microorganisms that respire back a lot of CO2,” Burman explained.
The team also observed plant physiology during the study with a hand-held device, and matched their observations with the results calculated using physics-based models.
“After you get the carbon uptake, if a plant is taking up CO2, its biomass will grow. So you will see that in the plant growth. If you are taking a picture of the plant, you will see that in the pre-monsoon period, plants are bigger. In monsoon, they are not so big as compared to pre-monsoon,” Burman added.
As a next step, researchers are trying to fetch insights from Gross Primary Productivity (GPP) datasets. GPP measures the total carbon dioxide plants absorb from the air via photosynthesis over a certain period. The approach is to calculate uncertainties in ground-based and satellite-based observation.
“Over the Indian region, there was no data. But research was not stopped. People were still trying to project an Indian carbon cycle in future. And they were using the old secondary data sets. We are also validating those data sets and finding out how much uncertainty is in those data sets,” Burman said.
(Edited by Viny Mishra)